Tax Forms work as "read-only" with Reaction v3.1.0

[kieckhafer]

Issue Description

With the release of Reaction API v3.1.0, the tax forms on variants no longer work to update tax rates. They still display the correct data, and update correctly when using the taxRate mutations directly.

Steps to Reproduce

Please provide starting context, i.e. logged in as a user, configure a particular payment method.

1. Create a product
2. See that the tax rates on variants update correctly if using the mutation via GraphiQL
3. See that the form shows the updated version, but you can't update the tax rate from the form itself, you'll see this error:

03:12:06.945Z  INFO Reaction: Primary tax service calculation returned null. Using set fallback tax service

Possible Solution

Update the forms to use the GQL mutation when updating the rates.